Exam 2: Antimicrobial Introduction, Bacteria, and Susceptibility Testing

Question 1

What two bacteria are of greatest public health concern relative to food poisoning as it relates to veterinary use of antimicrobials?

Answer 1

Nontyphoidal Salmonella spp.

Campylobacter

Question 2

What is the connection between veterinary antimicrobial use and resistance nontyphoidal Salmonella spp and Campylobacter?

Answer 2

The concern is that the vet use, particularly in food animals, is influencing these pathogens
The most common way humans get salmonella and campylobacter is animals that have these bacteria and go to slaughter
The meat is contaminated, and it is not cooked properly by the consumer

Question 3

Explain what the term “four quadrant coverage” implies relative to antimicrobial utility for a patient

Answer 3

Helps cover everything for antimicrobials
Divides it into gram-positive and gram-negative as well as aerobes/facultative anaerobes and obligate anaerobes
This means the antibiotics you have chosen are effective against a vase majority of bacteria
Useful for a multi-etiologic infection

Question 4

Explain the differences between constitutive versus acquired resistance.

Answer 4

Constitutive resistance:
Gram negatives are resistant inherently to penicillin because their porins will not allow penicillin to enter.
Built into the anatomy and pathogenicity of the organism

Acquired resistance:
Bacteria have mutated to become resistant and those mutations have passed along to other bacteria by replication or plasmid transposon transfer
More important

Question 5

Describe vertical transmission of resistance genes

Answer 5

Mutation occurs, and clone reproduces

Question 6

Describe horizontal transmission of resistance genes

Answer 6

Predominate mechanism
Transfer of genetic material between bacteria
—Same species-plasmid
—Across species-transposon
Genes for multiple antimicrobial resistance often occur in “packets”
—To reduce resistance, you need to stop everything in the packet
Much greater impact

Question 7

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for E. coli?

Answer 7

Extremely prone to antimicrobial resistance

Question 8

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for Pasteurella?

Answer 8

Less resistance problems than enteric, but it depends on prior exposure to antimicrobials

Question 9

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for staph?

Answer 9

Huge problem with antimicrobial resistance

Question 10

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for strep?

Answer 10

Sensitive to penicillin G

Huge problem with antimicrobial resistance

Question 11

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for anaerobes?

Answer 11

Most anaerobes are similar to which antimicrobials they are resistant to, but there are 2 exceptions:
Fusobacteria is sensitive to a variety of antibiotics
Bacteriodes fragilis is resistant to many antimicrobials that other obligate anaerobes are sensitive to

Question 12

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for B. fragilis?

Answer 12

Resistant to many antimicrobials that other obligate anaerobes are sensitive to

Question 13

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for Rickettsia?

Answer 13

Reliably sensitive to certain drugs

Tetracycline is drug of choice

Question 14

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for Lepto?

Answer 14

Reliably sensitive to certain drugs

Question 15

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for Mycoplasma?

Answer 15

Certain antibiotics are available that mycoplasmas routinely respond to

Question 16

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for Chlamydia?

Answer 16

Emerging antibiotic resistance

Tetracyclines are used to treat

Question 17

What is the predictable susceptibilities to certain antibiotics such that in vitro susceptibility testing is often not performed for Pseudomonas?

Answer 17

Huge problem with antimicrobial resistance

Question 18

Is Bordetella enteric or nonenteric gram-negative?

Answer 18

Nonenteric gram-negative

Question 19

Is Citrobacter enteric or nonenteric gram-negative?

Answer 19

Enteric gram-negative

Question 20

Is E. coli enteric or nonenteric gram-negative?

Answer 20

Enteric gram-negative

Question 21

Is Enterobacter enteric or nonenteric gram-negative?

Answer 21

Enteric gram-negative

Question 22

Is Haemophilis enteric or nonenteric gram-negative?

Answer 22

Nonenteric gram-negative

Question 23

Is Klebsiella enteric or nonenteric gram-negative?

Answer 23

Enteric gram-negative

Question 24

Is Mannheimia enteric or nonenteric gram-negative?

Answer 24

Nonenteric gram-negative

Question 25

Is Pasteurella enteric or nonenteric gram-negative?

Answer 25

Nonenteric gram-negative

Question 26

Is Proteus enteric or nonenteric gram-negative?

Answer 26

Enteric gram-negative

Question 27

Is Salmonella enteric or nonenteric gram-negative?

Answer 27

Enteric gram-negative

Question 28

Is Serratia enteric or nonenteric gram-negative?

Answer 28

Enteric gram-negative`

Question 29

Which organism is often deemed as one of the most aggressive relative to tissue destruction?

Answer 29

Pseudomonas

Question 30

Which one cannot be removed by filtration for sterilization of liquids?

Answer 30

Mycoplasma

Question 31

Which gram-negative obligate anaerobe tends to be the most susceptible to antimicrobials?

Answer 31

Fusobacteria is often very sensitive to a variety of antibiotics

Question 32

Where do enterococci normally reside on the body?

Answer 32

Commonly found in feces

Question 33

How do enterococci compare to beta-hemolytic streptococci relative to their antibiotic susceptibility?

Answer 33

Enterococci have a huge antimicrobial resistance

Question 34

What is the relative pathogenicity of enterococci in surface wounds?

Answer 34

Not aggressively pathogenic in surface wounds

Question 35

Of the two major species of enterococci, which is the most common and which is the most likely to have multiple drug resistance?

Answer 35

Most common is Enterococcus faecalis

More prone to resistance problems in Enterococcus faecium

Question 36

What are the primary staphylococcal species causing infection in man, dog, cow, horse, and pig?

Answer 36

Staph (pseudo)intermedius is major pathogen in dogs

Staph. aureus is a major pathogen in bovine mastitis, pigs, and man

Question 37

Describe MIC

Answer 37

Amount of antibiotic necessary to inhibit growth (not kill) of a microorganism
Most commonly employed in vitro technique
Rule of thumb:
1. For bactericidal antimicrobials, the MBC is within one or two dilutions of the MIC
2. For bacteriostatic antimicrobials, the MBC is often greater than 100X the MIC
Quantitative results

Question 38

Describe MBC

Answer 38

Amount of antibiotic to kill 99.9% of all organisms
Rely on the host to finish of the bacteria
This value must be used when treating immunocompromised patients

Question 39

Describe E-test

Answer 39

Strip has different concentrations of antibiotic
There are more concentrations on this that microtiter panel
This is more of a research technique

Question 40

Describe break-point panels

Answer 40

This test for susceptibility, Intermediate, and resistant
Tells you the same thing as Kirby bauer
Qualitative results

Question 41

Describe Kirby Bauer agar diffusion

Answer 41

Organism is streaked out and placed on disc
Different antibiotic concentrations are placed on plate
The chemical characteristics are the determining factor of how the zones occur, so you can’t compare zones

Question 42

Explain why in vitro susceptibility test results on milk, skin, and GI infections may indicate resistance when it does not exist.

Answer 42

We get much higher drug concentrations locally in these areas that we test on MIC
If milk is resistant, we must test mammary tissue as well
We can’t say that there is a good correlation of susceptibility results with these
If drug is susceptible, that can be trusted

Question 43

Describe concentration-dependent killing

Answer 43

Aminoglycosides have this
Peak concentration/MIC creates a ratio. If ratio is 8 or greater the cure rate was 91%
4-7.9 has a cure rate of 67% and 0-3.9 had a 10% cure rate
You want a high peak concentration, one that goes high above MIC

Question 44

Describe Area Under the Inhibitroy Curve

Answer 44

AUC in a 24-hour dosing interval/MIC
If it surpasses a certain threshold, we can have greater efficacy
Fluoroquinolones and some data for tetracyclines
If AUC/MIC was below 125, there’s only a 26% cure rate. Above 125, 82% cure rate (number varies with drug, disease, and patient)

Question 45

Describe time-dependent killing

Answer 45

Beta-lactams

Not how high it goes, but how long it stays above the MIC in a dosing interval